The present invention relates to articles provided with a water-repellent film coating formed integrally with an primary oxide film on the surface of a substrate made of glass, ceramic, plastic, metal or the like, to a water-repellent film-coating composition and to a process for preparation of water-repellent film-coated articles.
The following techniques for formation of highly durable water-repellent films on the surfaces of glass plates and other substrates at a high rate of productivity are known, which involve formation of a single film on a substrate using a mixed solution of a primary layer component and a water-repellent component which gives a primary layer and a water-repellent layer.
In Japanese Unexamined Patent Publication No. 4-338137 there is disclosed a water-repellent glass characterized by applying of a solution comprising a mixture of a silicon alkoxide or a substituted silicon alkoxide wherein a portion of the alkoxyl groups are substituted with fluoroalkyl groups, an alcohol, water and an acid (or base) onto a glass substrate surface and sintering.
In Japanese Unexamined Patent Publication No. 8-239653 there are disclosed water-repellent articles treated with a composition comprising a mixture of a perfluoroalkylalkylsilane and a thoroughly hydrolyzable silane (for example, tetrachlorosilane) dissolved in a solvent, preferably a non-aqueous solvent.
In Japanese Unexamined Patent Publication No. 11-71682 there are disclosed water-repellent film-coated articles treated with a composition comprising a chlorosilyl group-containing compound and a fluoroalkyl group-containing silane compound dissolved in an alcohol-based solvent.
In these conventional techniques, the final water-repellent article has been obtained by applying the coating solution onto the surface of the glass plate or the other substrate and then sintering at a temperature of 100-250xc2x0 C. which is lower than the decomposition temperature of the fluoroalkyl groups (250-300xc2x0 C.), or simply drying at ordinary temperature. The films obtained by these techniques are known as sol-gel water-repellent films and are obtained through a process whereby a hydrolyzable silane compound and a silane compound with a water-repellent group are hydrolyzed in a solution, subjected to dehydration/condensation reaction and then coated and dried on a substrate; in the sol-gel film, however, the solvent progressively evaporates as oxide bonds are formed, and therefore fine pores are present in the film when it is dried at 400xc2x0 C. or below, so that the film does not have high hardness. In order to avoid the pores for increased film hardness, it has been essential to accomplish sintering at 500-600xc2x0 C. However, heating at such high temperatures results in decomposition of the fluoroalkyl groups, making it impossible to achieve the desired water repellency. Consequently, water-repellent films obtained by the aforementioned technique of sintering at 250xc2x0 C. or below, while being composed mainly of oxides, have not had the high hardness as oxides and ceramics which is achieved by, for example, melt methods.
When such water-repellent film-coated articles are used outdoors, for example, their exposure to such conditions as blown sand readily results in damage to the film surface, thus impairing the water-repellent property. The water-repellent film can also be damaged or peeled when the surface is wiped with a cloth or the like to remove attached dust, dirt or sand. Even in the absence of attached dust, etc., abrasion with a cloth or brush made of hard fibers (such as surface wiping of automobile window glass with a wiper, for example) forms small nicks and further promote deterioration of the water-repellent film.
It is an object of the present invention, which has been accomplished in light of these problems, to provide articles coated with high-performance water-repellent films having high hardness that can withstand outdoor use, a process for preparation of such water-repellent film-coated articles at a high rate of productivity, and a coating liquid composition for preparation of such water-repellent film-coated articles.
As a result of much diligent research by the present inventors aimed at overcoming the aforementioned problems, it has been discovered that by providing a primary oxide film with two or more components including SiO2 and at least one type selected from among MgO, CaO, SrO and B2O3 in a water-repellent film-coated article having a primary oxide layer and a water-repellent layer integrally formed by a single coating treatment, the hardness of the water-repellent film with the integrally formed primary layer and water-repellent layer is drastically improved.
In other words, the present invention relates to a water-repellent film-coated article comprising a substrate and a water-repellent film composed mainly of silicon oxide and having a water-repellent group coated on the surface of the substrate, the water-repellent film-coated article being characterized in that the water-repellent film contains at least one type of metal oxide selected from the group consisting of magnesium oxide, calcium oxide, strontium oxide and boron oxide.
For formation of oxide films by a sol-gel method it is common to use a silicon alkoxide as the starting material, and this is because the reactivity of silicon alkoxides readily gives a uniform, transparent film by a milder reaction than with alkoxides of elements other than silicon. However since, as mentioned above, the solvent progressively evaporates as bonds (siloxane bonds) are formed between the Si (silicon) and O (oxygen) by dehydration/condensation reaction in the sol-gel method, a porous silica film is obtained wherein fine pores are present in the film. Since the Si and O bonds are covalent bonds and Si and O bond with a high bonding energy, when siloxane bonds form a somewhat three-dimensional structure at the solvent volatilization stage, contraction of the structure is suppressed even with subsequent further dehydration/condensation reaction, such that a volatilized portion of the solvent and the alcohol produced by the dehydration/condensation reaction remains as fine pores, with silanol or unreacted alkoxyl groups present in the fine pores. The hardness of the porous silica film is not very high because of its porosity. When the film is heated at a temperature of 500xc2x0 C. or above, the fine pores in the film disappear producing a non-porous silica film with high hardness, but it is difficult to form an integral film with high hardness containing substances that decompose at the heating temperature.
According to the invention, the strong ionic nature of magnesium (Mg), calcium (Ca) and strontium (Sr) is utilized: they are dissolved in the coating solution to be copresent with the thoroughly hydrolyzable silane compound, such as a silicon alkoxide, and exist in an ionic state in the solution even at the solvent volatilization stage. Because Mg, Ca and Sr are divalent, they react with silanol, eventually bonding with two oxygen atoms in the film interior as shown in Equation (1), and forming an xe2x80x9cOxe2x88x92 +M+ xe2x88x92Oxe2x80x9d bond which has a freer bonding orientation than an xe2x80x9cSixe2x80x94Oxe2x80x94Sixe2x80x9d bond, to thereby fill in the gaps of the siloxane skeleton. 
When simply dried at normal temperature, for example, this film has about the same hardness as if a silica component alone was used, but heating at a temperature of 50-300xc2x0 C. contracts the siloxane bonds by action of the Mg (or Ca or Sr), and this eliminates pores and results in a film with high hardness and high durability comparable to inorganic glass prepared by a melt method. That is, while heating at a temperature of 500xc2x0 C. or above is necessary to eliminate the pores of a simple porous silica film, the porous silica-based film of the invention which contains MgO, CaO or SrO can be rendered pore-free at a temperature of 200xc2x0 C. or more below that temperature. Furthermore, since the film is heated at a temperature lower than the decomposition temperature of the water-repellent groups such as fluoroalkyl groups or alkyl groups (300xc2x0 C. or higher), the fluoroalkyl groups or alkyl groups contained in the coating solution reside on the film surface without decomposition, thus providing excellent water repellency and durability. When only a silica component with water-repellent groups is present, the film has insufficient hardness and low durability with heat hardening at 300xc2x0 C. or below, and heating at a temperature of 500xc2x0 C. or above is necessary to eliminate the film pores and increase the film hardness, which in turn sacrifices the high water repellency.
Addition of an oxide of boron (B) to the silica also provides a low temperature hardening property and gives a pore-free film with high hardness by heating at a temperature of 300xc2x0 C. or below, as with addition of Mg, Ca or Sr described above. While it is not yet fully understood why B exhibits a similar effect as Mg, Ca and Sr, it is thought to be attributable to a change in the configuration of oxygen due to the heating immediately after coating.
If the content of magnesium oxide, calcium oxide, strontium oxide and boron oxide in the water-repellent film is too low the low temperature hardening effect will not be obtained, while if it is too high the oxides will segregate to a non-uniform condition, thus lowering the film hardness; the water-repellent film therefore preferably contains silicon oxide, magnesium oxide, calcium oxide, strontium oxide and boron oxide in the following proportions, based on SiO2, MgO, CaO, SrO and BO3/2, respectively:
silicon oxide at 70-99%, and
at least one type of metal oxide selected from the group consisting of magnesium oxide, calcium oxide, strontium oxide and boron oxide at a total of 1-30%,
in terms of mole percent; the water-repellent film also preferably contains silicon oxide, magnesium oxide, calcium oxide, boron oxide and zirconium oxide in the following proportions, based on SiO2, MgO, CaO, BO3/2 and ZrO2, respectively:
silicon oxide at 70-98%,
magnesium oxide and/or calcium oxide at 1-29%,
and boron oxide and/or zirconium oxide at 1-29%, in terms of mole percent.
Certain combinations among these give superior low temperature hardening properties. Specifically, they are the four combinations Sixe2x80x94Mgxe2x80x94B, Sixe2x80x94Caxe2x80x94B, Sixe2x80x94Mgxe2x80x94Zr and Sixe2x80x94Caxe2x80x94Zr. These sol-gel oxide films harden by, for example, heating at 200-250xc2x0 C. for films with a film thickness of about 150 nm and heating at about 100xc2x0 C. for films with a film thickness of a few dozen nm or less, giving water-repellent films with high hardness.
Thus, according to the present invention an oxide film of two or more components including silicon oxide and at least one type selected from among magnesium oxide, calcium oxide, strontium oxide and boron oxide as essential components is used as the primary oxide layer to allow elimination of pores from the primary oxide film at below the decomposition temperature of the water-repellent layer. Water-repellent film-coated articles obtained thereby have high hardness or durability that has not been possible in the past with water-repellent film-coated articles with integrally formed primary oxide layers and water-repellent layers by a single coating treatment.
The low temperature hardening property of the water-repellent film of the invention is not impaired even when a transition metal element or the like is further introduced into the silica film for the purpose of adding another function in addition to the water-repellent function, such as control of the refractive index of the film or control of the visible light transmittance. In other words, by including a metal element exhibiting a desired function along with the Mg, Ca, Sr or B it is possible to obtain a multifunctional film having very high hardness even with heating at a temperature of 300xc2x0 C. or below, while also having both water-repellent and other functions. For example, addition of cobalt oxide, iron oxide, nickel oxide or copper oxide will impart coloring to the water-repellent film.
When the water-repellent film of the invention contains zirconium oxide, it may include as other components cobalt oxide, iron oxide, nickel oxide, copper oxide, aluminum oxide, gallium oxide, indium oxide, scandium oxide, yttrium oxide, lanthanum oxide, cerium oxide and zinc oxide at a total of 0.5-5% in terms of mole percent, based on CoO, FeO3/2, NiO2, CuO, AlO3/2, GaO3/2, InO3/2, ScO3/2, YO3/2, LaO3/2, CeO3/2 and ZnO.
When the water-repellent film of the invention contains no zirconium oxide, it may include as other components cobalt oxide, iron oxide, nickel oxide, copper oxide, zirconium oxide, aluminum oxide, gallium oxide, indium oxide, scandium oxide, yttrium oxide, lanthanum oxide, cerium oxide and zinc oxide at a total of 0.5-5% in terms of mole percent, based on CoO, FeO3/2, NiO2, CuO, ZrO2, AlO3/2, GaO3/2, InO3/2, ScO3/2, YO3/2, LaO3/2, CeO3/2 and ZnO.
In either case, addition of these components at a total in excess of 5 mole percent may produce an undesirable appearance, such as film peeling or film whitening.
If the thickness of the water-repellent film is too great the film hardness will tend to be lower, and if it is too small the film durability will tend to be lower. The thickness of the water-repellent film is therefore preferably 5-200 nm, more preferably 5-100 nm and even more preferably 5-50 nm. The water-repellent film preferably contains the water-repellent groups, for example alkyl groups or fluoroalkyl groups, at 0.01-20 wt %. The water-repellent groups are present at a high density on the outer surface of the water-repellent film.
The present invention also provides a water-repellent film-coating composition containing
(A) a thoroughly hydrolyzable silane compound,
(B) a silane compound with a water-repellent group,
(C) an acid and
(D) at least one metal compound selected from the group consisting of magnesium, calcium, strontium and boron.
The thoroughly hydrolyzable silane compound (A) according to the invention is not particularly limited, and tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane and tetrabutoxysilane, as well as tetrachlorosilane, tetraacyloxysilane and tetraisocyanatesilane may be mentioned. Tetraalkoxysilanes are preferred for use among these because of their relative ease of handling. Among tetraalkoxysilanes, those of relatively low molecular weight, for example tetraalkoxysilanes comprising alkoxyl groups of 3 or fewer carbon atoms, are preferred for use because they readily give dense films. Also, polymers of these tetraalkoxysilanes, with average polymerization degrees of 5 or lower, are preferred for use.
The silane compound with a water-repellent group (B) according to the invention is a silane compound with one, two or more water-repellent groups (alkyl groups, fluoroalkyl groups, etc.) in the molecule, and there may be mentioned silane compounds which are the aforementioned silane compounds (A) a portion of which is substituted with an alkyl group and/or fluoroalkyl group.
Examples of alkyl group-containing silane compounds include alkyl group-containing chlorosilanes such as
CH3(CH2)30SiCl3, CH3(CH2)20SiCl3,
CH3(CH2)18SiCl3, CH3(CH2)16SiCl3,
CH3(CH2)14SiCl3, CH3(CH2)12SiCl3,
CH3(CH2)10SiCl3, CH3(CH2)9SiCl3,
CH3(CH2)8SiCl3, CH3(CH2)7SiCl3,
CH3(CH2)6SiCl3, CH3(CH2)5SiCl3,
CH3(CH2)4SiCl3, CH3(CH2)3SiCl3,
CH3(CH2)2SiCl3, CH3CH2SiCl3,
(CH3CH2)2SiCl2, (CH3CH2)3SiCl,
CH3SiCl3, (CH3)2SiCl2, (CH3)3SiCl;
alkyl group-containing alkoxysilanes such as
CH3(CH2)30Si(OCH3)3, CH3(CH2)20Si(OCH3)3,
CH3(CH2)18Si(OCH3)3, CH3(CH2)16Si(OCH3)3,
CH3(CH2)14Si(OCH3)3, CH3(CH2)12Si(OCH3)3,
CH3(CH2)10Si(OCH3)3, CH3(CH2)9Si(OCH3)3,
CH3(CH2)8Si(OCH3)3, CH3(CH2)7Si(OCH3)3,
CH3(CH2)6Si(OCH3)3, CH3(CH2)5Si(OCH3)3,
CH3(CH2)4Si(OCH3)3, CH3(CH2)3Si(OCH3)3,
CH3(CH2)2Si(OCH3)3, CH3CH2Si(OCH3)3,
(CH3CH2)2Si(OCH3)2, (CH3CH2)3SiOCH3,
CH3Si(OCH3)3, (CH3)2Si(OCH3)2, (CH3)3SiOCH3,
CH3(CH2)30Si(OC2H5)3, CH3(CH2)20Si(OC2H5)3,
CH3(CH2)18Si(OC2H5)3, CH3(CH2)16Si(OC2H5)3,
CH3(CH2)14Si(OC2H)3, CH3(CH2)12Si(OC2H5)3,
CH3(CH2)10Si(OC2H5)3, CH3(CH2)9Si(OC2H5)3,
CH3(CH2)8Si(OC2H5)3, CH3(CH2)7Si(OC2H5)3,
CH3(CH2)6Si(OC2H5)3, CH3(CH2)5Si(OC2H5)3,
CH3(CH2)4Si(OC2H5)3, CH3(CH2)3Si(OC2H5)3,
CH3(CH2)2Si(OC2H5)3, CH3CH2Si(OC2H5)3,
(CH3CH2)2Si(OC2H5)2, (CH3CH2)3SiOC2H5,
CH3Si(OC2H5)3, (CH3)2Si(OC2H5)2, (CH3)3SiOC2H5;
alkyl group-containing acyloxysilanes such as
CH3(CH2)30Si(OCOCH3)3, CH3(CH2)20Si(OCOCH3)3,
CH3(CH2)18Si(OCOCH3)3, CH3(CH2)16Si(OCOCH3)3,
CH3(CH2)14Si(OCOCH3)3, CH3(CH2)12Si(OCOCH3)3,
CH3(CH2)10Si(OCOCH3)3, CH3(CH2)9Si(OCOCH3)3,
CH3(CH2)8Si(OCOCH3)3, CH3(CH2)7Si(OCOCH3)3,
CH3(CH2)6Si(OCOCH3)3, CH3(CH2)5Si(OCOCH3)3,
CH3(CH2)4Si(OCOCH3)3, CH3(CH2)3Si(OCOCH3)3,
CH3(CH2)2Si(OCOCH3)3, CH3CH2Si(OCOCH3)3,
(CH3CH2)2Si(OCOCH3)2, (CH3CH2)3SiOCOCH3,
CH3Si(OCOCH3)3, (CH3)2Si(OCOCH3)2,
(CH3)3SiOCOCH3;
and alkyl group-containing isocyanatesilanes such as
CH3(CH2)30Si(NCO)3, CH3(CH2)20Si(NCO)3,
CH3(CH2)18Si(NCO)3, CH3(CH2)16Si(NCO)3,
CH3(CH2)14Si(NCO)3, CH3(CH2)12Si(NCO)3,
CH3(CH2)10Si(NCO)3, CH3(CH2)9Si(NCO)3,
CH3(CH2)8Si(NCO)3, CH3(CH2)7Si(NCO)3,
CH3(CH2)6Si(NCO)3, CH3(CH2)5Si(NCO)3,
CH3(CH2)4Si(NCO)3, CH3(CH2)3Si(NCO)3,
CH3(CH2)2Si(NCO)3, CH3CH2Si(NCO)3,
(CH3CH2)2Si(NCO)2, (CH3CH2)3SiNCO,
CH3Si(NCO)3, (CH3)2Si(NCO)2,
(CH3)3SiNCO.
Among these alkyl group-containing silane compounds it is preferred to use chlorosilanes, alkoxysilanes, acyloxysilanes and isocyanatesilanes containing alkyl groups of 8 or more carbon atoms, such as the following.
Octyltrimethyoxysilane CH3(CH2)7Si(OCH3)3,
octyltrichlorosilane CH3(CH2)7Si(Cl)3,
nonyltrimethoxysilane CH3(CH2)8Si(OCH3)3,
nonyltrichlorosilane CH3(CH2)8Si(Cl)3,
decyltrimethoxysilane CH3(CH2)9Si(OCH3)3,
decyltrichlorosilane CH3(CH2)9Si(Cl)3,
undecyltrimethoxysilane CH3(CH2)10Si(OCH3)3,
undecyltrichlorosilane CH3(CH2)10Si(Cl)3,
dodecyltrimethoxysilane CH3(CH2)11Si(OCH3)3,
dodecyltrichlorosilane CH3(CH2)11Si(Cl)3.
Examples of fluoroalkyl group-containing silane compounds include fluoroalkyl group-containing trichlorosilanes such as
CF3(CF2)11(CH2)2SiC3,
CF3(CF2)10(CH2)2Si(Cl)3,
CF3(CF2)9(CH2)2SiCl3,
CF3(CF2)8(CH2)2SiCl3,
CF3(CF2)7(CH2)2SiCl3,
CF3(CF2)6(CH2)2SiCl3,
CF3(CF2)5(CH2)2SiCl3,
CF3(CF2)4(CH2)2SiCl3,
CF3(CF2)3(CH2)2SiCl3,
CF3(CF2)2(CH2)2SiCl3,
CF3CF2(CH2)2SiCl3,
CF3(CH2)2SiCl3;
fluoroalkyl group-containing trialkoxysilanes such as
CF3(CF2)11(CH2)2Si(OCH3)3,
CF3(CF2)10(CH2)2Si(OCH3)3,
CF3(CF2)9(CH2)2Si(OCH3)3,
CF3(CF2)8(CH2)2Si(OCH3)3,
CF3(CF2)7(CH2)2Si(OCH3)3,
CF3(CF2)6(CH2)2Si(OCH3)3,
CF3(CF2)5(CH2)2Si(OCH3)3,
CF3(CF2)4(CH2)2Si(OCH3)3,
CF3(CF2)3(CH2)2Si(OCH3)3,
CF3(CF2)2(CH2)2Si(OCH3)3,
CF3CF2(CH2)2Si(OCH3)3,
CF3(CH2)2Si(OCH3)3,
CF3(CF2)11(CH2)2Si(OC2H5)3,
CF3(CF2)10(CH2)2Si(OC2H5)3,
CF3(CF2)9(CH2)2Si(OC2H5)3,
CF3(CF2)8(CH2)2Si(OC2H5)3,
CF3(CF2)7(CH2)2Si(OC2H5)3,
CF3(CF2)6(CH2)2Si(OC2H5)3,
CF3(CF2)5(CH2)2Si(OC2H5)3,
CF3(CF2)4(CH2)2Si(OC2H5)3,
CF3(CF2)3(CH2)2Si(OC2H5)3,
CF3(CF2)2(CH2)2Si(OC2H5)3,
CF3CF2(CH2)2Si(OC2H5)3,
CF3(CH2)2Si(OC2H5)3;
fluoroalkyl group-containing triacyloxysilanes such as
CF3(CF2)11(CH2)2Si(OCOCH3)3,
CF3(CF2)10(CH2)2Si(OCOCH3)3,
CF3(CF2)9(CH2)2Si(OCOCH3)3,
CF3(CF2)8(CH2)2Si(OCOCH3)3,
CF3(CF2)7(CH2)2Si(OCOCH3)3,
CF3(CF2)6(CH2)2Si(OCOCH3)3,
CF3(CF2)5(CH2)2Si(OCOCH3)3,
CF3(CF2)4(CH2)2Si(OCOCH3)3,
CF3(CF2)3(CH2)2Si(OCOCH3)3,
CF3(CF2)2(CH2)2Si(OCOCH3)3,
CF3CF2(CH2)2Si(OCOCH3)3,
CF3(CH2)2Si(OCOCH3)3;
and fluoroalkyl group-containing triisocyanatesilanes such as
CF3(CF2)11(CH2)2Si(NCO)3,
CF3(CF2)10(CH2)2Si(NCO)3,
CF3(CF2)9(CH2)2Si(NCO)3,
CF3(CF2)8(CH2)2Si(NCO)3,
CF3(CF2)7(CH2)2Si(NCO)3,
CF3(CF2)6(CH2)2Si(NCO)3,
CF3(CF2)5(CH2)2Si(NCO)3,
CF3(CF2)4(CH2)2Si(NCO)3,
CF3(CF2)3(CH2)2Si(NCO)3,
CF3(CF2)2(CH2)2Si(NCO)3,
CF3CF2(CH2)2Si(NCO)3,
CF3(CH2)2Si(NCO)3.
Among these fluoroalkyl group-containing silane compounds there are preferred trichlorosilanes, trialkoxysilanes and triisocyanatesilanes containing fluoroalkyl groups with 10 or more fluorine atoms, of which CF3(CF2)7(CH2)2Si(OCH3)3 (heptadecafluorodecyl trimethoxysilane) and CF3(CF2)7(CH2)2SiCl3 (heptadecafluorodecyl trichlorosilane) are particularly preferred.
The acid (C) according to the invention is preferably a volatile acid such as hydrochloric acid, hydrofluoric acid, nitric acid, acetic acid, formic acid, trifluoroacetic acid or the like from the standpoint of volatilization by drying at ordinary temperature without remaining in the film, and hydrochloric acid is particularly preferred among these because of its high degree of electrolytic dissociation and volatilization and its relative safety during handling.
At least one type of metal compounds selected from the group consisting of magnesium, calcium, strontium and boron (D) according to the invention may be any chlorides, oxychlorides, oxides, hydroxides, nitrates, oxynitrates, etc. of the aforementioned metals, so long as they undergo simple electrolytic dissociation to dissolve in water or alcohol. Among these, it is particularly preferred to use chlorides, oxychlorides, nitrates and oxynitrates.
Specific examples for component (D) include MgCl2, Mg(NO3)2, CaCl2, Ca(NO3)2, SrCl2, Sr(NO3)2 and H3BO3.
The zirconium oxide is not an essential component, but including it with the magnesium oxide or calcium oxide increases the low temperature hardening property, and therefore a zirconium compound, for example a chloride, oxychloride, oxide, hydroxide, nitrate or oxynitrate, which undergoes simple electrolytic dissociation to dissolve in water or alcohol, may be included in the water-repellent film-coating composition. Specific examples of such compounds include ZrOCl2 and ZrO(NO3)2.
As an additional component (component (E)) there may be added to the water-repellent film-coating composition at least one metal compound selected from the group consisting of cobalt, iron, nickel, copper, aluminum, gallium, indium, scandium, yttrium, lanthanum, cerium and zinc, such as a chloride, oxychloride, oxide, hydroxide, nitrate or oxynitrate of one or more of these metals, as the starting material for cobalt oxide, iron oxide, nickel oxide, copper oxide, aluminum oxide, gallium oxide, indium oxide, scandium oxide, yttrium oxide, lanthanum oxide, cerium oxide and zinc oxide, for the purpose of imparting the aforementioned functions of control of the refractive index of the film or control of the visible light transmittance. Any of these compounds are suitable so long as they dissociate in water or alcohol, and those that undergo simple electrolytic dissociation are especially preferred. In other words, it preferably decomposes without producing oxide precipitation, etc., and is present in the coating solution in an ion state.
Specific examples of the aforementioned component (E) include AlCl3, GaCl3, InCl3, ScCl3, YCl3, LaCl3, CeCl3, CoCl2, ZnCl2, Al(NO3)3, Ga(NO3)3, In(NO3)3, Sc(NO3)3, Y(NO3)3, La(NO3)3, Ce(NO3)3, Co(NO3)2, Zn(NO3)2.
The water-repellent film-coating composition preferably contains the silane compound (A) at 0.01-2 wt % based on silica, the silane compound (B) at 0.00001-0.15 wt % based on silica, the acid at 0.001-3 N, water at 0-5 wt %, the compound (D) at a molar ratio of 0.01-0.4 with respect to the silane compound (A), and the component (E) at a molar ratio of 0-0.4 with respect to the silane compound (A).
The solvent for the water-repellent film-coating composition is not particularly limited, but hydrocarbons such as hexane, toluene and cyclohexane, halogenated hydrocarbons such as methyl chloride, carbon tetrachloride and trichloroethylene, ketones such as acetone and methyl ethyl ketone, nitrogen-containing compounds such as diethylamine, esters such as ethyl acetate, and alcohols may be used. Preferred for use among these are alcohol-based solvents, examples of which include methanol, ethanol, 1-propanol, 2-propanol, butyl alcohol, amyl alcohol and the like among which straight-chain saturated monohydric alcohols of 3 or fewer carbon atoms, such as methanol, ethanol, 1-propanol and 2-propanol are even more preferred for use because of their high volatilization rates at ordinary temperature.
These alcohols may also contain water at from 0 wt % to 50 wt %. Commercially available high-grade alcohols usually contain water at 0.2 wt % or more, and according to the invention they are preferably used to avoid cost-raising treatments such as dewatering treatment. For addition of the metal starting materials, even when the metal compounds are added after first being dissolved in water, the amount of water in the final water-repellent film-coating composition may be 50 wt % or less with respect to the amount of solvent. The amount of water is preferably not greater than 50 wt % because this will prevent a uniform, transparent film from being formed.
A preferred water-repellent film-coating composition according to the invention contains
(A) a thoroughly hydrolyzable silane compound or its hydrolysate at 0.01-2 wt % (based on silica),
(B) a silane compound with a water-repellent group at 0.00001-0.15 wt % (based on silica),
(C) an acid at 0.001-3 N,
(D) at least one type of metal compound selected from the group consisting of magnesium, calcium, strontium and boron at a molar ratio of 0.01-0.4 based on MgO, CaO, SrO and BO3/2, with respect to the silane compound (A),
(E) at least one type of metal compound selected from the group consisting of cobalt, iron, nickel, copper, zirconium, aluminum, gallium, indium, scandium, yttrium, lanthanum, cerium and zinc at a molar ratio of 0-0.4 based on CoO, FeO3/2, NiO2, CuO, AlO3/2, GaO3/2, InO3/2, ScO3/2, YO3/2, LaO3/2, CeO3/2 and ZnO, with respect to the silane compound (A),
(F) water at 0-20 wt % and
(G) an alcohol constituting the remainder.
An even more preferred water-repellent film-coating composition contains
(A) a thoroughly hydrolyzable silane compound or its hydrolysate at 0.01-2 wt % (based on silica),
(B) a silane compound with a water-repellent group at 0.00001-0.15 wt % (based on silica),
(C) an acid at 0.001-3 N,
(D-1) a magnesium and/or calcium compound at a molar ratio of 0.01-0.4 based on MgO and CaO, with respect to the silane compound (A) (based on SiO2),
(D-2) a boron and/or zirconium compound at a molar ratio of 0.01-0.4 based on BO3/2 and ZrO2, with respect to the silane compound (A) (based on SiO2),
(E) at least one type of metal compound selected from the group consisting of cobalt, iron, nickel, copper, aluminum, gallium, indium, scandium, yttrium, lanthanum, cerium and zinc at a molar ratio of 0-0.4 based on CoO, FeO3/2, Nia2, CuO, AlO3/2, GaO3/2, InO3/2, ScO3/2, YO3/2, LaO3/2, CeO3/2 and ZnO, with respect to the silane compound (A) (based on SiO2),
(F) water at 0-20 wt % and
(G) an alcohol constituting the remainder.
The method of coating the water-repellent film-coating composition of the invention is not particularly limited, but preferably the substrate is evenly wetted with the coating solution composition and then stationed for drying to hardness. This allows formation of a highly oriented water-repellent layer as the fluoroalkyl groups and alkyl groups collect on the liquid surface during volatilization of the solvent. Here, the stationing is sufficient so long as the coating solution applied to the substrate is not disturbed, and the substrate may even be gently moved in a parallel direction during the application.
Specific examples of coating methods include dip coating, flow coating, curtain coating, spin coating, spray coating, bar coating, roll coating, brush coating and the like.
The drying according to the invention is carried out in an atmosphere at room temperature or a temperature of 300xc2x0 C. or below, and preferably at 40% or lower relative humidity. The coated state of the highly oriented surface is therefore maintained without decomposition of the integrally coated alkyl groups or fluoroalkyl groups. As a result it is possible to obtain a water-repellent film with a low temperature hardening property as well as excellent water-repellent performance including droplet roll-over properties and excellent durability due to its high hardness. Because of the low heating temperature, even when an alkali component is present in the substrate there is low diffusion thereof in the water-repellent film, thus preventing reduction in durability of the water-repellent property due the alkali.
As substrates for the invention there may be mentioned transparent and non-transparent plates, bars and other various forms of glass, ceramic, plastic or metal. When few hydrophilic groups are present on the surface of the substrate, it is preferred to pretreat the surface with an oxygen-containing plasma or corona atmosphere for hydrophilic treatment, or to irradiate the substrate surface with ultraviolet rays of a wavelength near 200-300 nm in an oxygen-containing atmosphere for hydrophilic treatment, followed by surface treatment.